1. Field of the Invention
The present invention relates generally to a sensor for fluoro species and to a method of sensing such species, having utility for monitoring of fluorine-containing compounds and ionic species in semiconductor process operations.
2. Description of the Related Art
In the manufacture of semiconductor devices, the deposition of silicon (Si) and silicon dioxide (SiO2), and subsequent etching, are vital operational steps that currently comprise 8-10 steps or roughly 25% of the total manufacturing process. Each deposition tool and etch tool must undergo a periodic cleaning procedure, sometimes as often as every run, in order to ensure uniform and consistent film properties.
Currently, in etching operations, etch endpoints are reached when a prescribed amount of time has elapsed. Over etch, in which the process gas continues to flow into the reactor chamber after the cleaning etch is finished, is common and leads to longer process cycles, reduced tool lifetimes, and unnecessary global-warming-gas losses to the atmosphere (Anderson, B.; Behnke, J.; Berman, M.; Kobeissi, H.; Huling, B.; Langan, J.; Lynn, S-Y., Semiconductor International, October (1993)).
Similar issues are present in the etching of silicon nitride materials when SiN is utilized in semiconductor device structures.
Various analytical techniques, such as FTIR, Optical Emission Spectroscopy, and Ionized Mass Spectroscopy, can be used to monitor the etch process. However, these techniques tend to be expensive, and often require a dedicated operator due to their complexity.
It would therefore be a significant advance in the art to provide a reliable, low-cost gas sensing capability that will serve to improve the throughput and chemical efficiency of the equipment used for the deposition and etching of silicon-containing materials, including silicon, silicon nitride and silicon dioxide, by reducing and optimizing clean and etch times, and hence reducing chemical usage, lengthening equipment operating life, and decreasing equipment down time.
In addressing this need, micromachined gas sensor devices would conceptually be useful to provide high performance sensing, due to their amenability to fabrication of suspended structures that can be manipulated thermally in a rapid manner. Surface micromachined devices have been developed using standard 2-level CMOS processing. In the fabrication of process sensors for aggressive environments, however, a major problem is protection of the sensor platform, particularly micromachined elements where SiO2 and/or Si3N4 membranes are employed, since these materials are rapidly etched in the process environment to which they are exposed to effect the sensing of the target gas component.
It would therefore be a significant advance in the art to provide a micromachined sensing device that is resistant to attack by the gas environment being monitored, e.g., where the gas environment to be monitored contains fluoro species or other corrosive agents or etchants.